Synthesis and Reaction of [{HC(CMeNAr)2}Mn]2 (Ar = 2,6-iPr2C6H3):  The Complex Containing Three-Coordinate Manganese(I) with a Mn−Mn Bond Exhibiting Unusual Magnetic Properties and Electronic Structure

This paper reports on the synthesis, X-ray structure, magnetic properties, and DFT calculations of [{HC(CMeNAr)2}Mn]2 (Ar = 2,6-iPr2C6H3) (2), the first complex with three-coordinate manganese(I). Reduction of the iodide [{HC(CMeNAr)2}Mn(μ-I)]2 (1) with Na/K in toluene afforded 2 as dark-red crystals. The molecule of 2 contains a Mn2 2+ core with a Mn−Mn bond. The magnetic investigations show a rare example of a high-spin manganese(I) complex with an antiferromagnetic interaction between the two Mn(I) centers. The DFT calculations indicate a strong s−s interaction of the two Mn(I) ions with the open shell configuration (3d54s1). This suggests that the magnetic behavior of 2 could be correctly described as the coupling between two S 1 = S 2 = 5/2 spin centers. The Mn−Mn bond energy is estimated at 44 kcal mol-1 by first principle calculations with the B3LYP functional. The further oxidative reaction of 2 with KMnO4 or O2 resulted in the formation of manganese(III) oxide [{HC(CMeNAr)2}Mn(μ-O)]2 (3). Compound 3 shows an antiferromagnetic coupling between the two oxo-bridged manganese(III) centers by magnetic measurements.